This invention relates generally to inclination switches, which respond to a change in inclination of an article to which the switch is mounted in order to actuate or deactuate a load. More particularly, the invention relates to an inclination switch for applications requiting long-term reliability notwithstanding repeated operation.
Inclination switches have many applications. In the automotive field, an inclination switch may be mounted to the lid of a trunk or engine compartment in order to actuate a light when the lid is raised and deactuate the light when the lid is lowered. Because, in such an application, the switch is actuated and deactuated with each opening of the trunk or engine compartment lid, industry standards require reliable operation for hundreds of thousands of actuation cycles.
Because of their reliability and freedom from moving mechanical contact components, which may experience erosion and welding from arcing, mercury switches have traditionally been used in such applications. However, with increased awareness of the environmental danger of mercury, such switches are typically prohibited in new product developments. As an alternative, switches have been proposed that incorporate a rolling ball positioned to selectively short a pair of contacts in response to inclination of the switch assembly. However, such devices tend to produce a noticeable rattle, or noise, upon actuation, which is considered a quality defect. Furthermore, the repeated breaking of current to the lamp eventually causes electrical erosion of the ball resulting in either intermittent malfunctioning due to contact stickiness or catastrophic malfunctioning by contact welding. Clearly such device is not a satisfactory substitution. Other designs, such as magnetically sensitive reed switches, in combination with gravity-positionable magnets, have been suggested but have proven to be unreliable and unduly expensive. Accordingly, there is a long-felt need for an inclination switch having the durability, reliability and quiet operation of mercury switches without their attendant environmental difficulties.